It would be a major advancement in the art if spacecraft and aircraft could be accelerated from standstill to a maximum allowable launch (takeoff) velocity under controlled g forces without using on board fuel and be able to recover all major elements of the system for reuse.
Spacecraft and aircraft have been conventionally launched either from a vertical or horizontal takeoff. The horizontal mode, well established for aircraft, requires completing an accelerating run along a runway to gain minimum launch velocity. The helicopter and NASA's well known space shuttle use the vertical takeoff mode. In both these modes, it is well known that the craft must use on board fuel very inefficiently to accelerate from a standstill. In the case of the space shuttle, the inefficiency leads to discarding expensive elements of its system without recovery.
NASA--in U.S. Pat. No. 4,265,416--overcomes some of the several objections to the space shuttle's vertical launch concept by mounting a space craft piggy back fashion on a pair of aircraft. The pair use their turbojet engines for a conventional takeoff run and then power the combination to a staging altitude. At staging altitude, the spacecraft separates and continues into orbit under its own rocket engine power. The pair of aircraft descend to a landing at its base. Unlike the shuttle, this two stage system recovers all the major components for reuse, however, it does not overcome the inefficient acceleration of the entire heavy system from a standstill to a minimum takeoff velocity with on board fuel. The accelerated weight includes the heavy on board fuel used for the acceleration as well as the heavy support structure for the fuel.
The British have proposed a reusable single stage unmanned launch system for a spacecraft.sup.2,8. This system would use a combination of air breathing and rocket engines. It would be launched from conventional runways used by commercial aircraft. Like the NASA system, this invention uses on board fuel to very inefficiently accelerate the entire load from a standstill to a minimum takeoff speed.
A proposal to lift a spacecraft to a staging altitude with a jet aircraft is envisioned by at least one potantial space entrepeneur.sup.6. The U.S. military uses variations of this concept to launch missiles from an aircraft to destroy vehicles in space. This concept also uses on board fuel to inefficiently accelerate the entire load from a standstill.
Other established methods for launching payloads into space include two stage expendable rocket powered vehicles used for deep space probes, but this costly procedure also inefficiently launches the vehicle from a standstill, using on board fuel.
Studies have been done on the electrothermal ramjet concept for propelling very small payloads into space.sup.3. This idea uses ramjet principles to accelerate a payload to escape velocity within a vertical tube mounted on a ground structure. The payload would encounter extremely high g forces (reportedly 3,000 to 30,000) and is limited to a maximum mass of about 10 kg. Obviously, these conditions limit the payload to a very few types.
All the concepts envisioned above are limited to launching payloads from within an oxygen atmosphere, such as earth has, with the exception of the conventional shuttle and the expendable rocket vehicles. All these concepts, including the shuttle and the expendable rocket vehicles, are imprctical for large scale operations on an airless world like the moon because of the large fuel requirements which are not readily available in a moon environment, at least not within the present state of the art.
The mass driver concept has been proposed for launching payloads into space .sup.4 . This is a catapult system similar in principle to the electrothermal ramjet idea except that the payload is accelerated along a guideway to escape velocity by magnetic force fields. The payload is not self propelling so it must reach escape velocity before leaving the force fields. It is proposed primarily for catapulting payloads from the surface of the moon where there is no atmospheric interference and the escape velocity is much less than on earth. Nevertheless, the payload mass is limited and the high g forces (reportedly 700 to 1,100) limits the type of payload. A human payload, for instance, would be hard pressed to survive 700 g.
An essential component of this invention is the magnetic propulsion of a magnetically levitated load along a guideway from a standstill to a high takeoff velocity. The idea of magnetic force fields to levitate and propel a load along a guideway has been known for many years.sup.1,9. This idea has been applied to train transportation.sup.1. Generally termed MAGLEV, it has successfully demonstrated accelerating a 224,000 pound vehicle to speeds of over 200 mph over a 20 mile test track.sup.10. A train holds the MAGLEV speed record of 321 mph and has the potential to reach 500 mph.sup.9. This speed record train was magnetically levitated four inches above its guideway.
Ground based MAGLEV technology uses two types of magnetic forces to levitate a load above a conducting guideway. There is the attractive magnetic force where two properly positioned magnets attract each other. One of these attractive magnets is held by the load and attracted upward to a magnet on a T shaped rail but does not touch it. This inherently unstable condition was used to safely accelerate the 224,000 pound vehicle mentioned above. The second type of force used is repulsive levitation caused by magnetic force fields between a magnet and, either, an induced field in a conductor or a second magnet of the same polarity. For practical reasons, the repulsive scheme uses a superconducting magnet in the vehicle to generate a very strong field. The conductor in the guideway can be coil or a continuous sheet. If the magnetic force at the surface of a continuous-sheet guideway is 20 kilogauss (about the strength at the pole face of a good magnet) the lift force is 60 pounds per square inch.sup.1. The MAGLEV speed record of 321 mph, mentioned above, used the repulsive with superconductors in the train.
For a practical guideway, using the repulsive method, lift begins at about 20 mph and is fully implemented, with the help of a wheeled support system, beginning at about 60 mph.sup.1,5. However, by electrifying the guideway, rather than relying on an induced field, the repulsive magnets could levitate at any speed.sup.5.
In both methods, attractive and repulsive, there is a separate set of magnets for propulsion. The load is propelled by alternating the currents in the moving magnets and the stator magnets in the guideway.sup.5. The frequency of alternating the currents must be synchronized with the speed of the load. This synchronization and the levitation became practical with the advent of computer controlled solid state switching devices.
MAGLEV technology for use in transportation is encountering obstacles in spite of its significant advantages such as low guideway maintenance, low running energy compared to auto and airplane.sup.11, etc. In addition to capital cost and skepticism, there are real technical obstacles that MAGLEV for train transportation encounters which are avoided with its use in the present invention.
______________________________________ U.S. PATENT DOCUMENTS ______________________________________ 4,265,416 5/1981 Jackson, et. al. 244-2 ______________________________________ OTHER PUBLICATIONS ______________________________________ 1. Scientific American, Oct 1973, pp. 17-25 2. Popular Mechanics, Feb 1985, pg. 74 3. Paper, "The Annular Flow Electrothermal Ramjet", B. D. Shaw, C. E. Mitchell & P. J. Wilbur, Jun 25, 1984, Colorado State Univ. 4. Science Digest, Jan 1985, pp. 59-61 5. High Technology, Sept 1984, pp. 34-36 6. Science Digest, Mar 1985, p. 49 7. Popular Science, Oct 1984, pp. 76, 77 8. Space World, Jan 1985, p. 19 9. Science 84, Aug, pp. 77-78 10. Popular Mechanics, Nov 1983, pp. 92-93 11. Quarterly Reports of the Railway Technical Institute, Vol 25, no. 1, Mar 1984, "Essential Techniques in MAGLEV transportation", pp. 13-18 ______________________________________